Use a class variable in a class method

Question

After I ran the code below, I got NameError: name 'result' is not defined. I tried to use class variable in a class method. Why does it give me an error?

class Test():
    def __init__(self):
        self.a=self.test1()
        self.result = Test.test2()+Test.test3()
    def test1(self):
        a=100
        return a

    result = Test.test3()+100
    @classmethod
    def test2(cls):
        b=200
        return b

    @staticmethod
    def test3():
        print("Testing3 is calling ")
        c=500+Test.result
        return c

Error:

result = Test.test3()+100
  File "<ipython-input-29-29d4025016c1>", line 18, in test3
    c=500+result
  NameError: name 'result' is not defined

self.result = Test.test3()+100 will not work. the problem comes from c=500+Test.result return c — Mike
– Mike, Commented Dec 3, 2021 at 19:27
Test.result is declared in the line result = Test.test3()+100, so how can it be declared at the time Test.test3() is being called? There is a circular reference. — kaya3
– kaya3, Commented Dec 3, 2021 at 19:31
I'd refer to this thread on how to properly use classmethod and staticmethod: stackoverflow.com/questions/12179271/… However beyond that, @kaya3 is right - you have other syntax issues here like the test.test3()+100 line — Jlove
– Jlove, Commented Dec 3, 2021 at 19:33
In your own words, where you have result = Test.test3()+100, what do you expect that to do, and when? Where you have c=500+Test.result, do you see how that depends on result = Test.test3()+100 having already occurred? Could it have already occurred? — Karl Knechtel
– Karl Knechtel, Commented Dec 3, 2021 at 19:34

Samwise · Accepted Answer · 2021-12-03 19:41:47Z

1

At the time the line of code in question is evaluated, result is not a class variable. It's been defined as an instance variable here:

    def __init__(self):
        self.a=self.test1()
        self.result = Test.test2()+Test.test3()

but the line of code that defines Test.result as a class variable:

    result = Test.test3()+100

has not yet finished executing at the time that it calls test3(), which itself has a dependency on Test.result.

answered Dec 3, 2021 at 19:41

Samwise

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